Bring an 8-quart pot of water to a boil. Immerse a quart-size canning jar, lid, and band in the water and boil for 10 minutes to sterilize. With tongs, transfer to a clean dishtowel to drain.

Boil the mushrooms in the water until tender, 10 minutes. Drain and pack them into the jar along with the thyme sprigs.

In a small saucepan, bring the vinegar, oil, sugar, peppercorns, bay leaf, garlic, chile, 1 Tbs. salt, and 1/2 cup water to a boil over medium heat. Pour the mixture over the mushrooms until it reaches the top of the jar. Screw on the lid, cool to room temperature, and refrigerate for 3 days before using. The mushrooms will keep in the refrigerator for at least 2 weeks.